This invention relates to an apparatus and method for performing an osteotomy. More particularly, but not by way of limitation, the invention relates to an apparatus and method for performing an osteotomy with an incrementally adjustable osteotomy fixation device. In this application, we describe its application to the most commonly performed osteotomy of the proximal tibia; however, the invention herein disclosed would apply to other bone or joint deformities.
All joints of the body, including the knee, are vulnerable to physical injury such as dislocation, fracture and/or damage by diseases such as arthritis and osteoporosis. As will be appreciated by those of ordinary skill in the art, a knee osteotomy is a procedure in which a section of bone is removed from either the upper tibia or distal femur in order to change the loading conditions at the knee. The knee osteotomy is generally performed by removal of a wedge of the bone so as to realign the remaining segments. A knee osteotomy may also be performed by adding a wedge of bone.
The osteotomy technique can serve to restore the anatomic and mechanical axes of the extremity. This operation is usually performed adjacent to the end of a bone, such as in the proximal region of the tibia, without removing the articular (end) surface, as would be the case for preparation of the bone for implantation of a joint prosthesis, such as a total knee prothesis. The procedure must be performed with a high degree of accuracy so that the end surface of the bone is not damaged and is subsequently correctly realigned to the desired orientation with respect to the alignment of the anatomic and mechanical axes of the bone.
An important consideration is the angle correction necessary for the reorientation. Prior art techniques of reorientation include cutting a predetermined wedge from the bone so as to leave intact a segment joining both portions of the bone. The bone portions are then drawn together to close the wedge shaped gap so that the sides there of engage. The bone portions may be secured and are allowed to heal in this new configuration.
In order to determine the angle correction, the geometry of the leg and the knee joint must be analyzed. Factors to consider for angular correction includes the forces affecting the knee joint (including but not limited to body weight, center of gravity, varus or valgus leg conditions, and the contact surface of the knee joint, etc). The magnitude and direction of forces acting upon the knee are a consequence of these and other factors. In the prior art, once these factors are considered, the angle and location of the osteotomy wedge may be chosen. Remember, the osteotomy changes the angle of the knee joint which in turn changes the distribution of forces along the contact surfaces of the joint.
The primary means of producing an angular correction to a joint include either a closing wedge or an opening wedge osteotomy. The closing wedge osteotomy does not work well because it decreases leg length and has a highly variable outcome. The prior art techniques used for a closing wedge osteotomy require that the surgeon create a wedge correction of a specific angle to make it conform to the bone during the initial osteotomy surgery. With this type of technique, all adjustments have to be made during the surgery. Once the wound is closed, no further changes can be made. This necessitates that all angular correction to the bone must be made during the initial surgery. The fixation device thus implanted will simply maintain that position until the bone heals. The opening wedge osteotomy works well if it is used in conjunction with external fixation hardware such as the Wagner method to provide adjustment during healing: However, this approach currently requires external fixation hardware to provide adjustments and this carries with its use the risk of infection. Further, external fixation is bulky and complicates the functional after care of a patient. Prior art devices for providing adjustment of an osteotomy during healing is the apparatus described by Robinson (U.S. Pat. No. 5,354,396). This device provides adjustment of the osteotomy site through an apparatus that extends through a patient's skin and therefore carries with its use the risk of infection and complications with regard to patient care. In addition, this device is designed for use on portions of the body that do not support body weight. Therefore, it would not be an effective approach to provide adjustment of an osteotomy about the knee. Another prior art device to provide adjustment of an osteotomy during healing is the apparatus described by Hildebrandt (U.S. Pat. No. 3,976,060). This device is fully implantable and has a self powered system to provide adjustment of the osteotomy site. Its purpose is to extend a bone and by virtue of its size it could not be used to provide angular adjustment of an osteotomy.
Thus, there is a need for an apparatus and method for performing a tibial osteotomy that will allow for greater accuracy for determining the correct angle of orientation. There is also a need for a procedure and device that provides for incremental adjustment of the angular correction through the healing process. There is also a need for a fully implantable device which can be adjusted using an external force (or brace). There is also a need for an apparatus that will allow for incremental adjustment following the surgery. Further, there is a need for incremental adjustability of the device that provides an opening wedge type of osteotomy with gradual distraction.